Methods and instruments for interbody fusion

ABSTRACT

A laparoscopic surgical technique is provided for preparing a site for implantation of a fusion device or implant. In accordance with one embodiment of the technique, a laparoscope is provided having an outer sleeve with distraction fingers at one end to distract the disc space. The laparoscope includes a laparoscopic port at its opposite end through which instruments and implants are inserted. The laparoscope provides a sealed working channel to the disc space, through which the disc space is distracted, the vertebral endplates and surrounding disc is reamed, and the fusion device inserted. The laparoscope is alternately engaged within bilateral locations in the disc space for insertion of a pair of fusion implants. A switching sleeve extends through the laparoscope to protect the tissue at the surgical site as the laparoscope is moved between the bilateral fusion locations.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of application Ser. No.08/411,017, filed on Mar. 27, 1995, now U.S. Pat. No. 5,782,919, namingthe same inventors and owned by the same assignee of the presentapplication.

The present invention relates to methods and instruments for performingan interbody fusion of a disc space between two adjacent vertebrae.Specifically, the invention concerns laparoscopic techniques andinstruments to prepare a fusion site and to insert fusion devices andimplants.

The number of spinal surgeries to correct the causes of low back painhas steadily increased over the last several years. Most often, low backpain originates from damage or defects in the spinal disc betweenadjacent vertebrae. The disc can be herniated or can be suffering from avariety of degenerative conditions, so that in either case theanatomical function of the spinal disc is disrupted. The most prevalentsurgical treatment for these types of conditions has been to fuse thetwo vertebrae surrounding the affected disc. In most cases, the entiredisc will be removed, except for the annulus, by way of a discectomyprocedure. Since the damaged disc material has been removed, somethingmust be positioned within the intra-discal space, otherwise the spacemay collapse resulting in damage to the nerves extending along thespinal column.

The intra-discal space is often filled with bone or a bone substitute inorder to prevent disc space collapse and to promote fusion of the twoadjacent vertebrae. In early techniques, bone material was simplydisposed between the adjacent vertebrae, typically at the posterioraspect of the vertebrae, and the spinal column was stabilized by way ofa plate or a rod spanning the affected vertebrae. Once fusion occurredthe hardware used to maintain the stability of the segment becamesuperfluous. Moreover, the surgical procedures necessary to implant arod or plate to stabilize the level during fusion were frequentlylengthy and involved.

It was therefore determined that a more optimal solution to thestabilization of an excised disc space is to fuse the vertebrae betweentheir respective end plates, preferably without the need for anterior orposterior plating. There have been an extensive number of attempts todevelop an acceptable intra-discal implant that could be used to replacea damaged disc and maintain the stability of the disc interspace betweenthe adjacent vertebrae, at least until complete arthrodesis is achieved.These “interbody fusion devices” have taken many forms. For example, oneof the more prevalent designs takes the form of a cylindrical implant.These types of implants are disclosec in the patents to Bagby, U.S. Pat.No. 4,501,269; Brantigan, U.S. Pat. No., 4,878,915; Ray, U.S. Pat. Nos.4,961,740 and 5,055,104; and Michelson, U.S. Pat. No. 5,015,247. Inthese cylindrical implants, the exterior portion of the cylinder can bethreaded to facilitate insertion of the interbody fusion device, asrepresented by the Ray, Brantigan and Michelson patents. In thealternative, some of the fusion implants are designed to be pounded intothe intra-discal space and the vertebral end plates. These types ofdevices are represented by the patents to Brantigan, U.S. Pat. Nos.4,743,256; 4,834,757 and 5,192,327.

Interbody fusion devices can be generally divided into two basiccategories, namely solid implants and implants that are designed topermit bone ingrowth. Solid implants are represented by U.S. Pat. Nos.4,878,915; 4,743,256; 4,349,921 and 4,714,469. The remaining patentsdiscussed above include some aspect that permits bone to grow across theimplant. It has been found that devices that promote natural boneingrowth achieve a more rapid and stable arthrodesis. The devicedepicted in the Michelson '247 Patent is representative of this type ofhollow implant which is typically filled with autologous bone prior toinsertion into the intra-discal space. This implant includes a pluralityof circular apertures which communicate with the hollow interior of theimplant, thereby providing a path for tissue growth between thevertebral end plates and the bone or bone substitute within the implant.In preparing the intra-discal space, the end plates are preferablyreduced to bleeding bone to facilitate this tissue ingrowth. Duringfusion, the metal structure provided by the Michelson implant helpsmaintain the patency and stability of the motion segment to be fused. Inaddition, once arthrodesis occurs, the implant itself serves as a sortof anchor for the solid bony mass.

Another interbody fusion device that is designed to permit bone ingrowthis shown in FIG. 1. This device is described and claimed in co-pendingparent application Ser. No. 08/411,017, filed on Mar. 27, 1995, whichdisclosure is incorporated herein by reference. In one embodiment, thisinvention contemplates a hollow threaded interbody fusion device 10configured to restore the normal angular relation between adjacentvertebrae. In particular, the device 10 as shown in FIG. 1 includes anelongated body 11, tapered along substantially its entire length,defining a hollow interior 15 and having a largest outer diameter at theanterior end 12 greater than the size of the space between the adjacentvertebrae. The hollow interior 15 opens at the anterior end 12 od thedevice to receive the bone growth material. The body 11 includes anouter surface 16 with opposite tapered cylindrical portions and a pairof opposite flat tapered side surfaces 22 between the cylindricalportions. Thus, at an end view, the fusion device gives the appearanceof a cylindrical body in which the sides of the body have been truncatedalong a chord of the body's outer diameter.

The cylindrical portions include threads 18 for controlled insertion andengagement into the end plates of the adjacent vertebrae. A starterthread 19 is provided at the posterior end 13 of the device 10 tofacilitate engagement within a prepared bore. The outer surface of thisfusion device is tapered along its length at an angle corresponding, inone embodiment, to the normal lordotic angle of lower lumbar vertebrae.The outer surface is also provided with a number of vascularizationopenings 24, 25 defined in the flat side surfaces, and a pair ofopposite elongated bone ingrowth slots 27 defined in the cylindricalportions.

Various surgical methods have been devised for the implantation offusion devices into a subject disc space. A patent to Dr. GaryMichelson, U.S. Pat. No. 5,484,437, discloses one such technique and theassociated instruments. As described in more detail in that patent, thesurgical technique involves the use of a hollow sleeve having teeth atone end that are driven into the adjacent vertebrae. These teeth and thesleeve maintain the disc space height during the subsequent steps of theprocedure. In accordance with one aspect of the invention in the '437Patent, a drill is passed through the hollow sleeve to remove the discand bone material to produce a prepared bore for the fusion device. Thedrill is then removed from the sleeve and the fusion device ispositioned within the disc space using an insertion tool.

In another aspect of the procedure and instruments disclosed in the '437Patent, a long distractor is provided having penetrating portions thaturge the vertebral bodies apart to facilitate the introduction of thenecessary instruments. The long distractor can act as a guide fordrilling and reaming tools concentrically advanced over the outside ofthe distractor to prepare the site for the fusion device.

While the Michelson technique represents a significant advance overprior surgical procedures for the preparation and insertion of fusiondevices, the need for improvement remains. In particular, procedures andinstruments that preserve the integrity of the surgical site aredesirable. The present invention is directed to this need in the field.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side perspective view of a threaded fusion device having atapered configuration to restore the normal angle of a spinal motionsegment.

FIG. 2 is a top elevational view of an implant driver for use inengaging and driving a fusion device such as the device shown in FIG. 1.

FIG. 3 is an enlarged perspective view of the end of the implant drivershown in FIG. 2 engaged to an fusion device such as shown in FIG. 1.

FIG. 4 is an enlarged side cross-sectional view of the implant driverand fusion device shown in FIG. 3.

FIG. 5 is an enlarged side cross-sectional view of an alternativeembodiment of an implant driver for engaging and driving a fusion devicesuch as the device shown in FIG. 1.

FIG. 6 is a driving tool attachment according to on aspect of thepresent invention.

FIG. 7 is an enlarged side cross-sectional view similar to the view inFIG. 5 with the driving tool attachment of FIG. 6 engaged between theimplant driver and the fusion device.

FIGS. 8(a)-(d) are lateral representations of the spine showing foursteps of a surgical method for implanting a fusion device such as thedevice in FIG. 1 according to an anterior approach in one aspect of thepresent invention.

FIGS. 9(a)-(d) are lateral representations of the spine showing foursteps of a surgical method for implanting a fusion device such as thedevice in FIG. 1 according to a posterior approach in further aspect ofthe present invention.

FIG. 10 is a frontal view of a patient with locations identified forsurgical incisions according to a preferred embodiment of the presentinventive laparoscopic surgical technique.

FIG. 11 is an A-P representation of a spinal segment at the laparoscopicsurgical site depicting one step of the inventive surgical technique inwhich bilateral locations are marked on the disc annulus for insertionof a pair of fusion devices, such as the device shown in FIG. 1.

FIG. 12 is an enlarged A-P view of the disc at the spinal segmentshowing the use of the template represented in FIG. 11 of the invention.

FIG. 13 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique of creatinga pilot hole at each of the bilateral locations marked in the step shownin FIG. 11.

FIG. 14 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique of using atrephine to create a bore at each of the bilateral locations marked inthe step shown in FIG. 11.

FIG. 15 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique forinserting a distractor into the prepared site at each of the bilaterallocations marked in the step shown in FIG. 11.

FIG. 16 is a perspective representation of the laparoscope according tothe present invention in which the outer sleeve of the laparoscope isengaged within the subject disc space.

FIG. 17(a) is a perspective representation of the laparoscope of FIG. 16with a switching sleeve according to one aspect of the inventiondisposed within the laparoscope.

FIG. 17(b) is an enlarged A-P representation of the laparoscope andswitching sleeve of FIG. 17(a) showing the positioning of a distractortip as depicted in FIG. 15.

FIG. 18 is a perspective representation of the laparoscope of FIG. 16with a reamer extending through the laparoscope to prepare the site forreceiving a fusion device.

FIG. 19 is is a perspective view of an implant driver of the type shownin FIG. 2 engaged to a fusion device and including a T-handle assemblyengaged to the driver.

FIG. 20 is a perspective view of an implant holder according to oneaspect of the present invention.

FIG. 21 is a perspective representation of the laparoscope used toimplant a bone dowel within the prepared site and including a bone dowelimpactor in accordance with one aspect of the present invention.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a driving tool assemblyfor implanting an interbody fusion device in the space between adjacentvertebrae is provided. The fusion device including a body has acylindrical outer surface interrupted by opposite non-cylindrical sidewalls, the outer surface having external threads defined thereon forthreading into the adjacent vertebrae. The tool assembly comprises adriving tool including an elongated shaft and a pair of opposite tongsconnected to one end of said shaft. The tongs are disposed apartrelative to each other to receive the opposite side walls of the fusiondevice therebetween. In accordance with the invention, a driving toolattachment includes a body having an outer surface and first and secondends. The body defines opposite non-cylindrical walls in its outersurface at the first end, with the walls configured for clampingengagement between the tongs of the driving tool. The body furtherdefines opposite flanges extending from its second end, the oppositeflanges having facing surfaces configured to engage the side walls ofthe fusion implant therebetween to impart a driving force from saiddriving tool attachment to the fusion implant when the driving toolattachment is engaged to said driving tool.

In another aspect of the invention, a method is provided for preparing asubject disc space for implantation of a fusion device or implantbetween adjacent vertebrae. In this technique, a laparoscope is providedthat includes an outer sleeve with opposite extensions at one end of theouter sleeve and a laparoscopic port engaged at the other end of theouter sleeve, the laparoscopic port having a number of seals, with theopposite extensions configured to maintain distraction of the adjacentvertebrae.

The preferred technique comprises the steps of making an incision in theskin of the patient aligned with the subject disc space, retractingtissue beneath the incision to expose the disc annulus; and piercing thedisc annulus to create an opening. The the outer sleeve of thelaparoscope is advanced through the incision, leaving the port outsidethe skin of the patient while inserting the opposite extensions into thedisc space with the outer sleeve contacting the disc annulus. Thelaparoscope, and particularly, the outer sleeve, creates a protectedworking channel between the disc space and the laparoscopic port outsidethe patient.

In a further step of the preferred inventive technique, a reamer isoperated through the number of seals and the outer sleeve of thelaparoscope to create a prepared bore in the disc material and theadjacent vertebrae for implantation of a device into the bore.

In a most preferred embodiment of the surgical technique, the techniquecomprises the steps of percutaneously exposing the annulus of the discin the subject disc space through an incision in the skin of the patientand piercing the disc annulus to create an opening. A distractor canthen be inserted through the incision and through the opening into thedisc space to distract the vertebrae adjacent the subject disc space.The laparoscope outer sleeve is then introduced through the incision andover the distractor, leaving the port outside the skin of the patientwhile inserting the opposite extensions through the opening into thedisc space to create the protected working channel between the port andthe distractor tip.

In subsequent steps, the distractor is removed and a reamer is advancedthrough the number of seals of the laparoscope and through the outersleeve into the disc space to ream the disc space and adjacent vertebraeto create a prepared bore for the fusion implant. After the reamer isremoved from the laparoscope, the fusion implant can be advanced throughthe number of seals and through the outer sleeve into the prepared bore.With the fusion implant in position, the laparoscope can be withdrawnfrom the patient.

In one aspect of the invention, a switching sleeve is palced within theouter sleeve of the laparoscope with an end of the switching sleeveprojecting beyond the opposite fingers of the outer sleeve, the end ofthe switching sleeve being tapered to minimize trauma to tissue adjacentthe subject disc space as the outer sleeve advanced into the patientwith the switching sleeve projecting beyond the opposite extensions ofthe outer sleeve.

In a further embodiment, the laparoscopic method is used for bilateralplacement of two fusion devices into a subject disc space. In additionto the steps previously described, this embodiment of the surgicaltechnique includes unseating the outer sleeve of the laparoscope fromthe first opening in the disc annulus by withdrawing the laparoscopeuntil the opposite extensions of the outer sleeve are outside the discannulus. With the switching sleeve in position within the outer sleeve,the laparoscope is moved to the second opening in the disc space withoutremoving the laparoscope from the patient. The steps for preparing thebore to receive a fusion implant can be repeated. In one specificembodiment, these steps are conducted at the second opening with thedistractor remaining within the first opening. After a fusion implantisnced through the number of seals and through the outer sleeve into thesecond prepared bores the laparoscope can then be returned to the firstopening for insertion of another fusion implant. During this step, thefusion implant contained within the second prepared bore maintainsdistraction of the disc space.

One object of the present invention is to provide surgical technique andinstruments that permit the preparation of a disc space for insertion ofa fusion implant under a sealed condition. A further object of theinvention is to implement laparoscopic techniques to implant fusiondevices.

One benefit of the present invention is that all of the steps necessaryto prepare a disc space and to implant a fusion device can be conductedin a protected environment. In addition, the inventive techniques andinstruments allow minimal intrusion into the patient, which minimizesthe risks normally associated with spinal surgery.

Other objects and benefits can be discerned from the following writtendescription and accompanying figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated devices, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

As described above, one interbody fusion device, as shown in FIG. 1, canbe implanted within the intra-discal space. This interbody fusion device10 can be implanted using the implant driver 50 shown in FIG.2. Theimplant driver 50 is comprised of a shaft 51 and sleeve 52concentrically disposed about the shaft. Tongs 54 are formed at one endof the shaft for gripping the interbody fusion device 10 forimplantation. Preferably the tongs include a tapered outer surface 55and an opposite flat inner surface 56 adapted to engage the truncatedside walls 22 of the interbody fusion device as shown in FIGS. 3, 4.Most preferably the tapered outer surface 55 conforms to the rootdiameter of the interrupted threads 18 of the device 10 so that thetongs 54 essentially complete the full cylindrical shape of the bodywall 16. The adaptation of the tongs' tapered outer surface 55facilitates screw insertion of the interbody fusion device 10 since theouter surface 55 will ride within the tapped bore in the vertebral endplates.

Each of the tongs 54 can be provided with interlocking fingers 58 and adriving projection 59 extending from the inner surface 56, most clearlyshown in FIG. 4. Referring again to FIG. 2, the shaft 51 defines a hingeslot 62 supporting each of the pair of tongs 54. The hinge slot 62 isconfigured so that the tongs will have a naturally biased positionspread sufficiently apart to accept the fusion device 10 therebetween.The shaft 51 defines a conical taper 63 between the hinged slot 62 andeach of the tongs 54. This conical taper mates with a conical chamfer 67defined on the inner wall of the sleeve 52. Thus, as the sleeve 52 isadvanced toward the tongs 54, the conical chamfer 67 rides against theconical taper 63 to close or compress the hinge slot 62. In this manner,the tongs 54 are pushed toward each other and pressed into grippingengagement with the interbody fusion device situated between the tongs.

The shaft 51 and sleeve 52 are provided with a threaded interface 65which permits the sleeve 52 to be threaded up and down the length of theshaft. Specifically, the threaded interface 65 includes external threadson the shaft 51 and internal threads on the sleeve 52 having the samepitch so that the sleeve can be readily moved up and down the implantdriver 50. The shaft 51 is also provided with a pair of stops 69 whichrestrict the backward movement of the sleeve 52 to only the extentnecessary to allow the tongs 54 to separate a sufficient distance toaccept the interbody fusion device 10.

The use of the implant driver 50 is shown with reference to FIGS. 3, 4.As can be seen in FIG. 3, the outer surface 55 of the tongs 54 residegenerally flush with the root diameter of the interrupted threads 18. Asseen in FIG. 4, the interlocking fingers 58 can be arranged to fitwithin the vascularization opening 24 on each of the truncated sidewalls 22. In a similar fashion, the driving projections 59 engage thedriving tool slots 29 at the anterior end 12 of the conical body 11. Thecombination of the interlocking fingers 58 and driving projections 59firmly engage the interbody fusion device 10 so that the device can bescrew threaded into a tapped or untapped opening in the vertebral bone.The tongs 54 in this embodiment are configured to engage the fusiondevice 10 and to impart a threading or rotational force to the device.It is understood that the tongs can adopt other configurations dependingupon the structure of the fusion device to be implanted.

An alternative embodiment of the implant driver is shown in FIG. 5. Thedriver 90 includes a shaft 91, having a length sufficient to reach intothe intra-discal space from outside the patent. Connected to the end ofshaft 91 is a head which defines a pair of opposite tongs 93, each ofwhich are configured for flush contact with the flat truncated sidewalls 22 of the fusion device 10. Like the tongs 54 of the previouslydescribed implant driver 50, the outer surface of the tongs iscylindrical to correspond to the cylindrical threaded portion of thedevice.

Unlike the implant driver 50, the driver 90 of the embodiment in FIG. 5uses an expanding collet assembly to firmly grip the fusion device 10for insertion into the body. Specifically, the head 92 defines a collet94 having a central collet bore 95 formed therethrough. The collet 94terminates in an annular flange 96 that at least initially has adiameter slightly smaller than the inner diameter of the fusion device10 at its end 12. An expander shaft 97 slidably extends through thecollet bore and includes a flared tip 98 situated adjacent and extendingjust beyond the annular flange 96. The flared tip 98 of the expandershaft 97 starts at a diameter sized to slide within the collet bore 95and gradually flares to a diameter larger than the bore.

The implant driver 90 further includes a puller shaft 99 slidablydisposed within a bore 100 defined in the shaft 91. The puller shaft 99has a locking chamber 101 at its end which engages a locking hub 102formed at the end of the expander shaft 97. The puller shaft 99 projectsbeyond the end of the shaft 91 for access by the surgeon. When thepuller shaft 99 is pulled, it pulls the expander shaft 97 away from theannular flange 96 of the collet 94 so that the flared tip 98 becomesprogressively engaged within the collet bore 95. As the tip 98 advancesfurther into the bore 95, the annular flange 96 expands from its initialdiameter to a larger second diameter sufficient for firm grippingcontact with the interior of the fusion device 10. With the fusiondevice so engaged, the implant driver can be used to insert the device10 into the surgical site, after which the expander shaft can beadvanced beyond the collet bore to release the flat tip and,consequently, the fusion device.

In certain circumstances it may be necessary to drive the fusion device10 deeper into the disc space. When either of the implant drivers 50 or90 is engaged to the fusion device, the device can be readily advancedfarther into the disc space. However, onse the implant driver is removedand it is then discovered that the fusion device needs to berepositioned, the flexible nature of the tongs 54 and 93 of the twoimplant drivers makes reacquisition of the now implanted fusion devicedifficult. To alleviate this difficulty, a driving tool attachment 120is provided, as shown in FIG. 6. The driving tool attachment 120includes a body 121 having a first end 122 and an opposite second end123. Like the fusion implant, the body 121 of the driving toolattachment 120 includes a cylindrical portion 125 and opposite flat sideportions 126. The opposite side portions 126 are configured to beengaged by the tongs of the above driving tools 50 or 90.

The driving tool attachment 120 includes a pair of opposing flanges 130at end 123. The flanges 130 are configured to engage the opposite flatsurfaces 122 on the fusion implant 10, in a manner similar to thataccomplished by the tongs of the implant driver 50 and 90. The end 123also includes a boss 131 which is configured to be inserted into theopening at the end of the implant 10 (see FIG. 7).

In use, the driving tool attachment 120 can be engaged with one of thedriving tools 50 or 90, with the tongs firmly grasping the flat surfaces126, as shown in FIG. 7. The driving tool attachment can then beadvanced into the disc space with the flanges 130 oriented across thespace so that they can readily interface with the flat surfaces 22 ofthe fusion device 10. When the driving tool attachment 120 is properlyaligned, the boss 131 projects into the hollow opening 15 at theanterior end 12 of the fusion device and the flanges 130 engage theopposite flat surfaces 22 of the device. The driving tool can then berotated as if the fusion implant were directly engaged to the maindriving tool. The attachment readily transmits the rotational drivingforce to the implant 10 to thread it deeper into the disc space or toretract it back within the disc space. One particular advantage providedby the driving tool attachment 120 is that the relatively flexible tongsof the two driving tools 50 and 90 can be already engaged to theattachment 120 before insertion into the surgical site. This eliminatesa great deal of fiddle factor and avoids the risk that the tongs wouldbe unable to firmly grasp the implant 10 when it is already in positionwithin the disc space.

In accordance with additional aspects of the present invention, twomethods for implanting an interbody fusion device, such as the device10, are contemplated. First, with reference to FIGS. 8(a)-8(d), ananterior approach is shown. As a preliminary step, it is necessary tolocate appropriate starting points for implanting the fusion device,preferably bilaterally. In the first step of the anterior approach, adistractor 75 is disposed between the vertebral end plates E to dilatethe L4-L5 or L5-S1 disc space. (It is understood, of course, that thisprocedure can be applied at other vertebral levels). In the second step,shown in FIG. 8(b), an outer sleeve 76 is disposed about the disc space.The outer sleeve 76 can be configured to positively engage the anterioraspect of the vertebral bodies to firmly, but temporarily, anchor theouter sleeve 76 in position. In essence, this outer sleeve 76 operatesas a working channel for this approach. In the step of FIG. 8(b), adrill 77 of known design is extended through the outer sleeve and usedto drill out circular openings in the adjacent vertebral bodies. Theopenings can be tapped to facilitate screw insertion of the fusiondevice 10, although this step is not necessary.

In the next step shown in FIG. 8(c), the fusion device 10 is engaged bythe implant driver 50 and extended through the outer sleeve 76 until thestarter thread 19 contacts the bone opening. The implant driver 50 canthen be used to screw thread the fusion device into the tapped oruntapped opening formed in the vertebral end plate E. It is understoodthat in this step, other suitable driving tools could be used, such as ascrew driver configured to engage the driving tool slots 29 at theanterior end 12 of the device 10. The degree of insertion of the fusiondevice 10 determines the amount of lordosis added or restored to thevertebral level. In the final step, the implant driver is removedleaving the fusion device 10 in position. It can be seen that onceimplanted, the closed posterior end 13 is directed toward the posterioraspect of the vertebrae. The hollow interior 15 is open at its anteriorend 12, but can be closed by a plastic or metal material, if necessary.

In a second inventive method, as depicted in FIGS. 9(a)-9(d), aposterior approach is implemented. The first two steps of the posteriorapproach are similar to that of the prior anterior approach, except thatthe distractor 75, outer sleeve 76 and drill 77 are introducedposteriorly at the instrumented motion segment. This approach mayrequire decortication and removal of vertebral bone to accept the outersleeve 76. In the third step of this method, the fusion device 10 isinserted through the outer sleeve 76 into the dilated disc space. It isunderstood that the disc space is preferably dilated only to the extentnecessary to receive the implant with the truncated side walls 22directly facing the vertebral end plates E. Thus, as shown in FIG. 9(c),the bone ingrowth slot 27 is facing laterally, rather than coronally, asexpected for its final implanted position. A suitable driving tool 80can be provided to project the fusion device 10 through the outer sleeve76 and into the intra-discal space. In one embodiment, the driving tool80 includes a projection 81 which is configured to engage a slot openingformed in the end wall at the posterior end 13 of the fusion device 10.An internal thread (not shown) can be used to fix the device 10 to thedriver 80.

Once the fusion device 10 has been advanced into the intra-discal spaceto the appropriate depth relative to the pivot axis P of the vertebrae,the driving tool 80 is used to rotate the implant in the direction ofthe rotational arrow R in FIG. 9(c). As the driving tool 80 is rotated,the device itself rotates so that the interrupted threads 18 startcutting into the vertebral bone at the end plates E. In this manner, theimplant operates as a cam to separate the adjacent vertebrae in thedirection of the spreading direction arrows S in FIG. 9(c). This cammingapproach provides a somewhat easier insertion procedure than for theanterior approach of FIGS. 8(a)-(d) in that a single rotation isrequired to lock the implant into the vertebral bone. In contrast, theformerly discussed screw insertion technique of the anterior approachrequires continuous threading of the device into position.

With either the anterior (FIGS. 8(a)-(d)) or the posterior approach(FIGS. 9(a)-(d)), the position of the fusion device 10 with respect tothe adjacent vertebrae can be verified by radiograph or other suitabletechniques for establishing the angular relationship between thevertebrae. Alternatively, the preferred depth of insertion of theimplant can be determined in advance and measured from outside thepatient as the implant is positioned between the vertebrae. The depth ofinsertion of the fusion device can be ascertained using depth markings(not shown) on the implant drivers 50, 90 or 80.

In another embodiment of the inventive surgical technique, laparoscopictechnology is used to provide a sealed and protected channel forinstruments and implants directed to the subject disc space. Inaccordance with one aspect of this inventive method, an anteriorapproach to the L5-S1 motion segment is illustrated. It is of courseunderstood that these same techniques and instruments to be describedbelow could be used at different vertebral levels or in a posteriorapproach under appropriate conditions.

As depicted in FIG. 10, the present inventive technique includes makinga small incision 140 and preferably inserting an insufflator needle intothe abdominal cavity. Fluid is introduced into the abdominal cavitythrough the insufflator needle to a pressure of preferably approximately15 mm of mercury to assist in visualization of the surgical site. Aninitial port 141 for the laparoscope is placed five to ten centimeterscephalad of the umbilicus in the midline ten millimeters in length. Theabdomen is visually explored and the patient is placed in steepTrandelenburg. The abdominal wall is visualized endoscopically as twoworking ports 142, 143 are placed just lateral to the epigastricvessels, opposite the level or levels to be fused. It is believed to beadvantageous to stagger the ports slightly from direct opposition toeach other.

The preferred method continues with insertion of retractors through theports 142, 143. The retractors can be used to sweep the small bowelsuperiorly out of the pelvis. The sigmoid colon is also pulled out ofthe pelvis and held laterally with the left fan retractor. For fusion atthe L5-S1 junction, the sacral promontory and drop-off can be easilyseen at this point. The posterior peritoneum overlying the L5-S1 discspace is then incised longitudinally with endoshears for the desiredexposure. Using opposing fan retractors as blunt dissectors, the softtissue underlying the parietal peritoneum can be swept laterally tobilaterally expose the anterior L5-S1 disc annulus. The sacral arteryand vein coursing the disc are individually ligated with hemoclips andtransected. A dissector can be used to remove residual soft tissue overthe disc. Exposure is maintained with the left fan retractor in placeholding the colon out of the way. It has been found that usually theright side does not require retraction, so a suction irrigation cathetercan be used through this port.

In one specific procedure for the L4-L5 disc, the posterior peritoneumis incised more proximally about 3 centimeters. Again, the left fan isused to retract the colon laterally and with careful blunt dissectionthe aorta is exposed anteriorly at the bifurcation. The L4-L5 disc isusually right below this point. Left lateral dissection is carried outover the left common iliac vein and artery, gently retracting thesevessels to the right. In order to retract these vessels enough to theright for adequate disc exposure the ascending segmental vein branchmust be identified and transected. Once this vessel is cut, the arteryand vein can then be bluntly retracted to the right with a fan or loopretractor to expose a significant amount of the L4-L5 disc for fusion.

Once the subject disc is exposed, it can be important to align theabdominal entry operating trocar port site 145 with the disc to be fusedso that the operating trocar is parallel with the endplates of the discin the sagittal plane. The entry point is estimated and a smallSteinmann pin can be placed either in the interspace or along thepatient and checked with lateral C-arm and adjusted accordingly. A 1.5to 2.5 centimeter incision can be made for placement of the operatingtrocar. A blunt introducer is placed in the abdomen and an 18 mm workingtrocar 147 (FIG. 11) can be placed over it under endoscopicvisualization.

In accordance with a further aspect of the present embodiment of thesurgical technique, the annulus of the subject disc D is marked forbilateral placement of a pair of fusion devices. For example, as shownin FIG. 11, a working trocar 147 is situated within the working port 145(see FIG. 10). The bilateral marks can be made with a template 150, asshown in FIG. 11 and in more detail in FIG. 12. Greater detailconcerning this template and its method of use can be found inco-pending application Ser. No. 08/427,432, filed on Apr. 24, 1995. Thedescription of this template in this co-pending application isincorporated herein by reference.

For convenience, a brief description of the template will be made withspecific reference to FIG. 12. In particular, the template 150 includestubular body 151 and an elongated guide foot 152 that is pivotablyconnected to the end 153 of the tubular body. A guide wire or stylet 155extends through the tubular body to pivot the foot 152 to the side. Thesharp tip 156 of the stylet can then be used to pierce the disc annulusD. Using a mallet, the template can be secured to the center of the discspace by driving the stylet 156 into the disc tangential to thecurvature of the annulus and parallel to the endplates. The template canthen be slid down the guide wire or stylet until the foot 152 contactsthe disc annulus.

The foot includes an opening 157 through which an electrocautery device160 can extend. The tip 161 of the electrocautery device is guidedthrough the opening 157 in the foot 152 to contact the disc annulus D.When the tip 161 is energized, it leaves a mark MR that is lateral tothe center of the subject disc. The template 150 can then be rotated inthe direction of the arrow T so that the foot is situated laterallyopposite the first mark MR. At that point, the electrocautery device canbe used to make a second mark ML providing the bilateral positions forthe two fusion devices.

Once the bilateral marks MR, ML have been made on the disc annulus, thesurgeon has a visual indication as to the proper location for placementof the fusion device. Under direct visualization of the insufflatedabdominal region by way of a laparoscope through port 141 (FIG. 10), thesurgeon can then direct a T-handle probe 160 through the working port147 to the either of the cauterization marks MR and ML. The T-handleprobe 160 includes a sharp tip 161 that is used to break through thedisc annulus. The T-handle allows the surgeon to rotate the probe 160 asnecessary to facilitate penetration into the annulus. Once an initialopening has been made in the disc annulus by way of the T-handle probe160, a T-handle trephine 165 can be used to create pilot holes forsubsequent instrumentation. The T-handle trephine 165 can include aseries of markings 166 at 5 mm increments to control the depth ofinsertion of the trephine into the disc space, as shown in FIG. 14. Themarkings 166 are compared to the working trocar 147 to gauge the depthof the cutting edge of the trephine, and therefore the depth of theprepared bore in the disc space and vertebral endplates. Again, theT-handle of the trephine allows the surgeon to rotate the trephine 165.This procedure is repeated at both of the electrocautery marks ML andMR. At this point, the surgeon has two bilateral holes to use fororientation during the remainder of the procedure. The trephine 165 isalso preferably used to core into the disc space to form bilateralbores. A rongeur may be used to clear disc material from each of thebilateral bores in the disc.

In accordance with further steps of the present inventive method, adistractor 167 is advanced through the working trocar 147 as shown inFIG. 15. The distractor has a distractor tip 169 that is selectedaccording to the vertebral level being instrumented. For instance,distractors for a 16 mm size implant can be either 12 mm or 14 mm inwidth to maintain the disc space at its proper anatomical height. Thetip 169 is removably attached to a distractor shaft 168. Preferably,progressively larger distractor tips are sequentially inserted inalternating fashion into each of the bilateral holes in the disc spaceand annulus until the annulus is taut and the adjacent vertebrae areadequately distracted for restoration of a proper disc space height. Inone aspect of the invention, the distractor tips 169, once they aredisposed in their bilateral positions, will act as a centering point oralignment guide for use of the instruments throughout the remainder ofthe procedure. It is therefore important that the distractor tips 169 beproperly located, which can be accurately confirmed with fluoroscopy.

Once the bilateral distractor tips have been properly seated, a shaftextension (not shown) can be engaged to distractor shaft 168. At thispoint, in accordance with the preferred embodiment, the disposabletrocar 147 is removed and a laparoscope 170 is introduced through theport 145 in the skin and into the disc space, using the distractor shaftand distractor tip as a positioning guide. In accordance with oneembodiment of the present invention, the laparoscope 170 includes anouter sleeve 171 having a first end 172 and a second end 173, as shownin FIG. 16. The second end 173 is engaged to a laparoscopic port 180which can be of conventional design. In particular, the laparoscopicport 180 can include a bore 184 (FIG. 17(a)) extending therethrough andin communication with the interior of the hollow outer sleeve 171. Thisbore 184 in the laparoscopic port allows introduction of instrumentsthrough the port and into the outer sleeve 171. The bore is preferablyclosed by a number of seals 182, which are configured to acceptcylindrical tools and instruments therethrough while maintaining tightsealed engagement about the instrument.

The laparoscopic port 180 also preferably includes a trumpet valve 183,which can be of conventional design. Specifically, the trumpet valve 183maintains the laparoscopic port 180 in a normally closed position inwhich its internal bore is closed from communication with the outersleeve 171. However, once an instrument is introduced into the port 180through the seals 182, the trumpet valve 183 moves aside to allowpassage of the instrument or tool into the sleeve 171.

In a further unique aspect of the invention, the end 172 of the outersleeve 171 includes a pair of opposite distraction extensions or fingers173. These distraction fingers 173 are sized according to the height ofthe particular disc space. Specifically, the fingers 173 are intended tomaintain the spacing between the adjacent vertebrae during subsequentsteps of the procedure after the distractor tip 169 has been removed.Thus, the width of the fingers 173 can be varied depending upon theparticular vertebral level being instrumented. In addition, thedistraction fingers 173 can be tapered to conform to a normal anglebetween adjacent vertebrae at the instrumented level. The position ofthe fingers 173 is correlated with the position of the distractor tipswithin the bilateral bores in the disc space by aligning the fingers 173with the trumpet valve 183 when the port 180 is engaged to the outersleeve 171. When the laparoscope 170 is inserted, the trumpet valvesprovide a visual indication of the alignment of the fingers. In otherwords, when the trumpet valve 183 is lateral to the midline, the fingers173 are properly oriented between the vertebral endplates.

In one specific embodiment, the outer sleeve 171 can include oppositespikes 174 disposed between the distraction fingers 173. These spikesare preferably configured to penetrate at least partially into theadjacent vertebral bodies, to help maintain the position of the outersleeve 171 at the surgical site. In some instances, the outer sleeve 171does not include the teeth 174. For example, where the procedure is toimplant a tapered fusion device, the teeth 174 are preferably eliminatedand where the device is a uniform cylinder, the teeth can be retained.

In one embodiment of the present surgical method, the laparoscope 170can be directly inserted over the distractor shaft extension (notshown). However, it is believed that the distraction fingers 173 and thespikes 172 can cause trauma to the skin during entry and to the softtissue surrounding the surgical site during introduction of thelaparoscope 170. Thus, a further feature of the preferred embodimentincludes a switching sleeve 190, as shown in FIGS. 17(a),(b). Theswitching sleeve 190 has a length sufficient to span the entire lengthof the laparoscope 170 from the port seals 182 to the end 172 of theouter sleeve 171. In particular, the switching sleeve 190 has a taperedtip 191 configured to extend beyond the end 172 of the outer sleeve 171,and more particularly beyond the ends of the fingers 173. The switchingsleeve 190 also includes a flared tip 192 at its opposite end that isenlarged to prevent its passage through the laparoscopic port 180 andparticularly the seals 182.

In accordance with a preferred embodiment of the inventive surgicalprocedure, the switching sleeve 190 is placed inside the laparoscope 170prior to insertion into the patient. The switching sleeve 190 has anouter diameter nearly equal to the inner diameter of the outer sleeve171 to slide in close running fit within the laparoscope 170. Thelaparoscope 170 and switching sleeve 190 can then be slid over thedistractor shaft and with a twisting motion pass through the skin andfascia until the outer sleeve contacts the disc annulus. It is importantto consider that the opposite fingers 173 on the outer sleeve 171 of thelaparoscope must pass through the opening in the disc space and bealigned between the adjacent vertebrae. As the fingers 173 are pushedinto the disc space, the switching sleeve 190 will remain outside thedisc annulus as its tapered tip 191 contacts the annulus in the regionbetween the distraction fingers 173 (see FIG. 17(b)). The outer sleeve171 of the laparoscope 170 is properly oriented when the fingers 173 arecorrectly oriented between and contacting the adjacent vertebraendplates. The outer sleeve 171 is then seated by striking a driving cap(not shown) mounted on the laparoscopic port, to thereby drive thefingers 173 fully into the disc space between the vertebral endplatesand to drive the spikes 174 into the adjacent vertebrae.

With the laparoscope 170 in place, all of the remaining steps of thisinventive technique occur under a relatively protected or sealedenvironment. Specifically, the outer sleeve 171 of the laparoscopeprovides a sealed passageway from the bilateral bores at locations MRand ML on the disc to the laparoscopic port 180 outside the patient. Thelaparoscope 170 can be used as a passageway to provide irrigation andaspiration where necessary, without the risk of fluids leaking into thespace adjacent the operative site. Moreover, the sealed working channelto the prepared sites in the disc space prevent leakage of abdominaldistension fluids into the working channel and disc space. This latteraspect allows direct vision of the surgical site outside the workingchannel created by the laparoscope.

With the laparoscope 170 in position, the distractor shaft 168 isremoved as well as the distractor tip 169 that is disposed between theadjacent vertebrae. Since the fingers 173 of the laparoscope outersleeve 171 will maintain the spacing between the adjacent vertebrae, thedistractor tip is no longer needed. Preferably, the surgeon will firmlygrasp the outer sleeve 171 as the distractor tip is being removed fromthe disc space to prevent dislodgement of the outer sleeve. In abilateral procedure, the bilateral bores in the disc each contain adistractor tip. In the preferred method, the right distractor tip isremoved first while the distractor tip in the left bore remains inplace. Thus, the fingers 173 of the laparoscope engaged within one ofthe bilateral locations share the distraction load with a distractor tip169 disposed within the other bilateral location. When the right side ininstrumented with a fusion device, as described below, the fingers 173will be within the left bore in the disc and will share the distractionload with the fusion device.

With the distractor tip removed and the disc space supported by thefingers 173, the next step in the inventive method is the preparation ofthe vertebral end plates and disc to provide a site for insertion of afusion device. The switching sleeve 190 is first removed and, inaccordance with one aspect of the invention, a reaming sleeve 195 isadvanced through the laparoscope 170. As shown in FIG. 18, the reamingsleeve 195 includes spikes 196 that are adapted to penetrate theadjacent vertebral bodies to hold the reaming sleeve in place. Oneobject of the reaming sleeve in this embodiment is to help maintain theposition of the laparoscope while the disc material and vertebral endplates are being reamed. This object is of particular importance whenthe laparoscope outer sleeve 171 does not include the teeth 174. Inaddition, the spikes 196 on the reaming sleeve 195 will prevent thevertebral bodies from being pushed away or distracted while reaming,since the force generated by the reamer can have a tendency to drive thevertebral bodies apart. This force is particularly present when atapered fusion device is to be implanted, necessitating cutting conicalthreads into the vertebra.

In accordance with the invention, an adjustable reamer 197 is extendedthrough the reaming sleeve 195. The reamer 197 can be of conventionaldesign with a cutting surface configured to evacuate the disc space andprepare the adjacent vertebral bodies to receive a threaded implant. Thereamer 197 includes an adjustable depth stop 198 disposed adjacent thelaparoscopic port 180. The depth stop 198 contacts the seals 182 of theport to prevent introduction of the reamer 197 too deeply into the discspace. The depth of reaming necessary, and consequently the position ofthe depth stop 198, can be determined prior to this reaming step byreview of fluoroscopic images.

The reamer 197 is manually operated by way of a T-handle 199 tosuccessively remove disc tissue and bone from the adjacent vertebralbodies to provide a prepared bore for the fusion implant. Preferably,several passes will be made with the reamer, after which the outersleeve will be examined visually and fluoroscopically to verify that itremains fully seated within the disc space. In addition, the reamingshould be observed under C-arm imaging to prevent reaming into thespinal canal. Preferably, the depth stop 198 will be set at an initialdrilling depth less than the anticipated full depth for implantinsertion. For example, for an L5-S1 fusion, a 20 mm deep reamed boremay be prepared for a 26 mm long implant.

After the disc material and vertebral bodies have been reamed by thereamer 197, one prepared site is available for insertion of the fusionimplant at the right location MR. It is then necessary to prepare theother bilateral location previously marked using the template 150(location ML in FIG. 12). In the next steps of the inventive method, thereamer 197 is withdrawn as well as the reaming sleeve 195. Thelaparoscope 170 is then unseated in a controlled manner so that thefingers 174 are disengaged from between the vertebrae and withdrawnthrough the opening of the disc annulus. However, the laparoscope 170,and particularly the outer sleeve 171, is not removed from the skinafter unseating from the disc space. Instead, the outer sleeve isreoriented over the second bilateral location ML (see FIG. 12).Preferably, immediately after the outer sleeve 171 is disengaged fromthe disc annulus, the switching sleeve 190 is extended back through theouter sleeve 171 so that the tapered end 191 of the sleeve extendsbeyond the fingers 173. The switching sleeve will then protect the softtissue surrounding the instrumented disc space as the outer sleeve 171is repositioned over the second bilateral location ML.

With the laparoscope 170 oriented over the second location ML and withthe switching sleeve 190 contacting the disc annulus, a distractor tip169 attached to a distractor shaft 168 is extended through the outersleeve 171. In the preferred technique, the laparoscope is not yet fullyseated at this location ML. The distractor tip 169 is advanced throughthe bore within the disc and anchored between the adjacent vertebral endplates. The laparoscope 170, and particularly the outer sleeve 171, isreseated within the disc space in the manner described above, namelywith the distraction fingers 173 disposed between the vertebral endplates. Once the position of the outer sleeve and fingers 173 isconfirmed using fluoroscopy, the remaining steps for preparing thevertebral bodies to receive the fusion implant are repeated at the leftlocation ML.

Once the second bore in the disc space has been prepared, the followingsteps of the technique involve insertion of the implant. In accordancewith the present invention, the implant can be a fusion cage of the typeshown in FIG. 1 which is tapered to restore the normal curvature at theparticular vertebral level. In the case of a fusion cage of the typeshown in FIG. 1, the implant driver 50 can be used to implant the device10. The implant driver 50 can be substantially as depicted in FIG. 2 andcan engage the implant 10 as shown in FIG. 3. In accordance with thepresent technique, the implant driver 50 can be engaged by a T-handleassembly 200, as shown in FIG. 19. The T-handle assembly 200 includes acollet 201 which engages the end of the implant driver 50 opposite thegripping tongs 54. The assembly 200 also includes T-handle 202 which isaligned with the gripping tongs 54 so that the surgeon has a visualindication of the orientation of the tongs 54 when the implant driver 50is extended through the laparoscope 170.

In accordance with the preferred technique, the implant driver 50carrying the fusion device 10 is inserted through the laparoscopic port180 and through the outer sleeve 171 until the implant 10 contacts theprepared bore within the disc space. At that point, the implant driver50 can be rotated using the T-handle 202 to thread the implant into theprepared bore. The implant driver 50 can preferably include a pluralityof depth markings on the driver shaft 51 beneath the collet 201 to givethe surgeon the visual indication of the depth of insertion of theimplant 10 into the prepared bore. Once the implant has been screwed into its predetermined depth, as indicated by the depth markings on theimplant driver shaft 51, insertion of the implant should be halted withthe T-handle 202 parallel to the vertebral end plates. With thisorientation of the T-handle 202, the tongs 54 of the implant driver 50will be exposed to the disc space, rather than in contact with thevertebral bone. Consequently, then the long slots 27 (see FIG. 1) of thefusion device 10 will be directly exposed to and in contact with thevertebral bodies.

With a fusion device 10 implanted within the left location ML, theimplant driver is removed from the implant and the laparoscope 170 isunseated from the left bilateral location. Again, the laparoscope 170 isnot removed from the skin after unseating, but is simply moved to thenext bilateral location MR, preferably with the switching sleeve 190protecting the surrounding tissue from the distraction fingers 173 ofthe laparoscope. At this location, the same steps are repeated toimplant a second fusion device 10 at this right location.

When each of the implant devices 10 is bilaterally implanted within thedisc space, the position of the implants should be confirmed. In someinstances, it may be necessary to reposition an implant within the discspace, such as by driving it further into the disc space. In thisinstance, the driving attachment 120 can be engaged to the implantdriver 50 and the attachment 120 engaged with the implanted device 10 topermit additional manipulation of the device.

In switching between the left location RL and the right location MR, itis preferred that the implant driver 50 be fully removed from thelaparoscope 170 and the switching sleeve 190 extended through the outersleeve 171. Also, the distractor tip 169 attached to the distractorshaft 168 should then be extended through the switching sleeve 170 andthe distractor tip can be used to locate the previous bore at the rightlocation MR. Once the distractor tip 169 is situated within the bore,the outer sleeve 171 can be seated at the right most location in thedisc space. With the outer sleeve 171 properly seated, the distractorshaft can be removed to make way for the implant driver 50 carrying anew implant fusion device 10. Of course, the switching sleeve is removedprior to extending the implant and implant driver through the outersleeve 171.

Once both fusion devices are disposed in their bilateral positions atlocations ML and MR, an A-P radiograph can be taken to assure properplacement. In addition, where possible, it is preferred that additionalbone graft material is packed around the implants in situ to furtherfacilitate fusion.

As discussed above, the fusion device 10 includes a hollow opening 15 toreceive bone growth material. In one specific embodiment, this bonegrowth material can include autogenous bone harvested from the patient'santerior iliac crest. Autograft bone from other locations, autologousbone, allograft, bone growth substitutes or other bone material capableof promoting or inducing bone ingrowth can be loaded into the implant.In the preferred technique, the interior 15 of each fusion implant 10 isfilled prior to insertion of the implant into the disc space.

To facilitate this “pre-loading” of the fusion material, an implantholder 210 is provided in accordance with the invention. This holder 210includes a base 211 that includes a fixed clamp section 212 and amovable clamp section 215. The fixed clamp section 212 includes a flange213 projecting from the base 211. The movable clamp section includes animpactor plate 216 that slides within a groove 217 formed in the base211. The impactor plate 216 is connected by a threaded shaft 218 to aknob 219. The threaded shaft is rotationally supported by an upstandingflange 221 attached to the base 211. The upstanding flange 221 includesa threaded bore (not shown) through which the threaded shaft 218extends. As the knob 219 is rotated, the shaft rotates within thethreaded bore of the flange 221 to move the impactor plate 216 forwardtoward the fixed clamp half 212.

In accordance with the present embodiment, a pair of blocks 225 and 226are provided which are disposed adjacent a corresponding one of clampsections 212 and 215. The blocks 225 and 227 include implant engagementsurfaces 226 and 228 which are configured to match the outer shape ofthe implant at its large slots 27. These blocks, therefore, serve toclose off the slots 27 as bone growth material is packed into theopening 15 of the implant 10. In one specific embodiment, the blocks 225and 227 are formed of plastic to effectively seal the large openings 27in the sides of the implant 10. Once the bone growth material has beentightly compacted within the implant device 10, the knob 219 can berotated in the opposite direction to release the movable clamp 216 fromthe device 10.

In accordance with another aspect of the present invention, thelaparoscope 170 can be used to implant a bone dowel 240, as depicted inFIG. 21. The bone dowel 240 can be of a variety of configurations, suchas an allograft Crock dowel, autograft tricortical or button dowels,manufactured composite dowels or hybrid dowels (e.g., an autogeneuosbutton combined with al allograft Crock dowel). While it is preferablethat the bone dowel 240 be cylindrical, this configuration is notessential to the invention, provided the dowel is configured to passeasily through the outer sleeve 171 of the laparoscope.

In accordance with this embodiment, the disc space and adjacentvertebral bodies are prepared as described above (see, FIGS. 10-18 andaccompanying text). In the preferred technique for implanting a bonedowel, the reamer 197 is used to create a partially cylindrical cut inthe vertebral endplates to receive a cylindrical dowel. Alternatively,if a non-cylindrical dowel is used, the endplates can be preparedaccordingly. It is understood that the dowel will typically have auniform outer diameter or width corresponding to the disc space height.Unlike the fusion device 10 discussed above the bone dowel is nottapered; however, preparation of the vertebral bodies with the tapereddistraction fingers 173 of the outer sleeve 171 providing an appropriateangle will allow the implanted bone dowel to retain this angle.

Once the disc space and vertebral endplates have been prepared toreceive the dowel, the bone dowel 240 is dropped into the laparoscopethrough outer sleeve 171. Due to the precise fit between the bone doweland the vertebral endplates, resistance will be experienced duringinsertion of the dowel. An impactor 245 is provided to drive the dowelinto its prepared site. The impactor includes an impactor head 246 thatis prefereably threaded engaged to an impactor shaft 247. The head andshaft are sized for a close running fit through the outer sleeve 171.Preferably, the impactor head 246 can be provided in several diametersdepending upon the size of the bone dowel to be implanted. Alsopreferably, the impactor shaft 247 will have a smaller diameter so thatit can be used with impactor heads and outer sleeves of severaldiameters.

The impactor shaft 247 includes a driving cap 248 that can be strickenby a hammer or similar tool to drive the bone dowel into the preparedsite in a controlled manner. Preferably, the impactor shaft alsoincludes a series of depth markings 249 corresponding to the depth ofinsertion of the bone dowel 240 into the disc space. The final positionof the dowel can be verified later by A-P radiograph. The second bonedowel can be inserted in a similar manner and additional bone graftplaced between the bilateral bone dowels.

The present invention involves instruments and surgical techniquesusable at any level of the spine. For simplicity, the above discussionhas focused on fusion of the L5-S1 disc space. The dimensions of each ofthe components of the instruments would be sized appropriately for thespecific vertebral level being instrumented. For example, the fusiondevices 10 may be offered in several sizes, including 12 mm, 14 mm and16 mm. Based upon the size of the fusion implant, the trephine 165 canbe provided in several sizes, such as trephines to form bores having adiameter of 6 mm, 8 mm or 10 mm.

The distractor tips 169 are also sized according to the size of thefusion device to be implanted. Preferably, the distractors are smallerthan the fusion device. For example, for a 16 mm fusion device, thedistractor tips 169 can be either 12 mm or 14 mm. For a 16 mm fusiondevice, a 16 mm reaming sleeve is provided to accept a 16 mm reamer toprepare a hole of the same diameter within the disc space and vertebralbodies. Smaller reamers and reaming sleeves would be provided forsmaller fusion devices. As previously described, the outer sleeve 171 ofthe laparoscope 170 is preferably a 2 mm in diameter to readily acceptall of the instruments and sleeves passing therethrough during theseveral steps of the inventive procedure.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A driving tool assembly for implanting aninterbody fusion device in the space between adjacent vertebrae, thefusion device including a body having a cylindrical outer surfaceinterrupted by opposite non-cylindrical side walls, the outer surfacehaving external threads defined thereon for threading into the adjacentvertebrae, said tool assembly comprising: a driving tool including; anelongated shaft; a pair of opposite tongs connected to one end of saidshaft, said tongs disposed apart relative to each other to receive theopposite side walls of the fusion device therebetween; and means forbiasing said tongs together to apply a gripping force therebetween; anda driving tool attachment including a body having an outer surface andfirst and second ends, said body defining opposite non-cylindrical wallsin said outer surface at said first end, said walls configured forclamping engagement between said tongs of said driving tool, and saidbody further defining opposite flanges extending from said second end,said opposite flanges having facing surfaces configured to engage theside walls of the fusion implant therebetween to impart a driving forcefrom said driving tool attachment to the fusion implant when saiddriving tool attachment is engaged to said driving tool.
 2. The drivingtool assembly according to claim 1, in which the fusion device includesan opening at one end, and wherein said driving tool attachment includesa boss defined at said second end of said body between said flanges,said boss configured to be received within the opening of the fusiondevice when said flanges engage the side walls of the fusion device.